Christopher Duffy 
The Fortress in the Age of Vauban and Frederick the Great 1660-1789 [PDF ebook] 

The later seventeenth and eighteenth centuries have been acclaimed as the classic period of artillery fortification. This was an era when fortresses and fortress systems shaped the calculations of strategists and statesmen, and often dictated the course of campaigns. The age was one of almost constant conflict and this book, originally published in 1985, explores the influence of the fortress in the dynastic wars of Bourbon, Habsburg and Hohenzollern, the contest for influence in the Baltic, the last crusades of the West against the Turks, and in the peculiar conditions of colonial campaigning and the War of the American Independence.